This invention relates to novel copolymers of itaconic acid with acrylic or methacrylic acid, a process for their preparation and their use as antiscalants.
Aqueous systems containing dissolved mineral salts are commonly employed in operations such as heating, cooling and evaporative distillation which involve heat transfer. The salts often become insoluble during the operation and are deposited as scale on the heat transfer surfaces, resulting in reduced heat transfer and eventual failure of the equipment. In general, the mineral scale salts are derived from alkaline earth and other metal cations such as calcium, magnesium, iron and lead, and from anions such as bicarbonate, carbonate, hydroxide, sulfate and phosphate. Many factors influence scale formation and include, for example, the pH of the water, the nature of the dissolved salts and the temperature of the operation.
Numerous additives have been proposed as inhibitors of mineral scaling. Of special importance are those additives known as threshold scale control agents which exhibit scale inhibition at extremely low additive concentrations of even one part per million or less. Included among the threshold scale control agents are acrylic and methacrylic acid homopolymers and copolymers with such as maleic anhydride and fumaric acid. While these additives have proven to be effective at threshold concentrations, their preparation generally involves use of nonaqueous solvent systems which are costly and which introduce the problem of solvent contamination of the polymer product. The need therefore still exists for effective threshold scale control agents which can be simply and inexpensively prepared in such as aqueous solvent systems.
(Meth)acrylic acid/itaconic acid copolymers have been prepared in the past in aqueous systems, but the use of such copolymers as scale inhibitors has not been disclosed. Thus, the (meth)acrylic acid/itaconic copolymer of U.S. Pat. No. 3,308,067 is used as a detergent builder, while that of U.S. Pat. No. 3,366,509 is intended as a sizing agent and the copolymer of U.S. Pat. No. 3,507,647 is employed in lithographic printing. Published United Kingdom Application GB2054548A discloses the use of a (meth)acrylic acid/itaconic acid copolymer in removing boiler scale. Both Marvel et al, J. Org. Chem., 24, 599 (1959) and Nagai et al, Kobunshi Kagaku, 17, 748 (1960) disclose methods of preparing (meth)acrylic acid/itaconic acid polymers but fail to mention a use for the resulting copolymer. All of these disclosed preparations involve a conventional copolymerization employing an aqueous medium and standard initiator system which results in copolymers of relatively high molecular weight.
It is therefore a primary objective of the present invention to provide a novel process for the preparation of substantially homogeneous (meth)acrylic acid/itaconic acid copolymers of controlled low molecular weight which are particularly effective as threshold scale inhibitors.